1. Field of the Invention
The present invention relates to a vacuum pump that is connected to equipment such as an electron microscope, or a container, and used for sucking in a gas from the equipment.
2. Description of the Related Art
Conventionally, vacuum pumps used for evacuating a gas from equipment such as an electron microscope, from a container, or the like possess an inlet port portion having an inlet port formed on one end of a casing that houses an evacuation function portion, and an exhaust port portion formed on the other end. The inlet port portion is connected to external equipment or the like through piping or the like, and a gas from the outside is introduced to the inside of the casing from the inlet port portion. The following may be given as an example of the exhaust function portion housed in the inside of the casing: a rotor portion and a stator portion may be disposed, and an outer circumferential surface of one of the rotor portion and the stator portion may be arranged as opposing an inner circumferential surface of the other portion, forming a gas transport portion for transporting a gas between the rotor portion and the stator portion. The rotor portion may then be made to rotate by a driving means such as a motor, and a gas from the outside may be sucked in by transporting the gas in the gas transport portion to the exhaust side. With turbo molecular pumps, one type of vacuum pump, stator blades that project out toward the rotor portion are provided in the stator portion, for example. On the other hand, rotor blades that project out between the stator blades are provided in the rotor portion. Gas molecules are hit by the rotating rotor blades, and transported. Furthermore, screw threads are formed on one circumferential surface from among mutually opposing circumferential surfaces of a rotor portion and a stator portion in screw thread type pumps. Gas is transported due to rotation of a rotor, utilizing the viscosity of the gas. Further, there are also turbo molecular pumps that combine these two types.
Gas suction force is obtained by rotationally driving the rotor portion with the aforementioned vacuum pumps, and not a small amount of vibration is generated along with the rotation. The vibration propagates from the casing to the external equipment through the inlet port portion, the piping, and the like. Functionality and endurance of the external equipment is adversely affected due to the vibration. For example, there is a large influence on microscopic images in an electron microscope due to even a minute amount of vibration. Various types of measurements for improvements have been developed in order to prevent these vibrations from propagating from the vacuum pump to the external equipment and the like. For example, an improved vacuum pump was proposed in Utility Model Application 58-119648. This vacuum pump is characterized in that an inlet port portion that is a portion for connecting to an apparatus is separated from a casing, and the inlet port portion is coupled to the casing through an elastic member and sealing means, thus reducing the propagation of vibrations from the vacuum pump body to the apparatus. Further, a rubber member and an O-ring or a bellows can be given as the elastic member and the sealing means, respectively.
However, there are problems such as the following with conventionally improved vacuum pumps.
1-1 Piping or the like on the vacuum pump is in a hanging state when connected to external equipment, and therefore, the weight of the vacuum pump except for the inlet port portion acts on the elastic member and the bellows, generating permanent deformation in the elastic member and the bellows, if the inlet port portion is connected to an apparatus. In the worst case, there is a fear that fracture will occur, and therefore a supporting means for supporting the vacuum pump, except for the inlet port portion, from the outside is necessary.
1-2 During vacuum pump operation, if the rotating body breaks and an overly large load acts on the vacuum pump body due to causes such as impacts and vibration from the outside, creep and corrosion of the rotating body, and the mixing in of foreign matters from the apparatus to the inside of the vacuum pump, then the elastic member and the sealing means coupled to the inlet port portion and the vacuum pump body (casing) may break, the airtightness of the inside of the vacuum pump may be harmed, the connection of the vacuum pump body to the apparatus may be lost, and there is a fear that this may cause the vacuum pump to run wild, leading to a significant accident.
1-3 For cases in which a rubber member is used as the elastic member, a compressive load is added to the rubber member by the pressure difference between the inside and the outside of the vacuum PUMP If this results in a state in which the rubber member is compressed too much, then the modulus of longitudinal elasticity and the modulus of transverse elasticity of the rubber member will become larger due to the properties of the rubber portion, and the vibration reducing characteristics will be deteriorated.
With the aforementioned circumstances as a background, an object of the present invention is to provide a vacuum pump capable of satisfactorily maintaining the vibration reducing characteristics of an elastic member, capable of preventing fracture and damage to the elastic member and to a sealing member, and in addition, able to prevent accidents from happening due to the pump running wild.